Air brake systems are known in the prior art and have been used in freight train braking systems for a number of years. For various reasons, it is particularly desirable that the air brakes of multiple cars in a train be applied and released generally uniformly and substantially instantaneously. Among these reasons are to deter and, if possible, eliminate property damage, bodily injury, and even possible loss of life which might occur as a result of non-uniform and/or sequential (that is, "domino effect") application and/or release of brakes among the various cars. Such non-uniform and sequential brake application and/or release can, if it becomes exaggerated, lead to damage of cars, derailment, significant property damage, and even personal injury or loss of life.
A rudimentary air brake comprises a piston housing having a piston disposed reciprocally therein. The piston stem is stepped to accommodate a graduating valve and to provide for engagement, by a shoulder of the piston stem, of a slide valve, both of which are received within the housing. Fluid communication exists between the housing, at a location remote from an end of the housing into which air from a brake pipe is introduced, and an auxiliary reservoir.
During normal operation of the train, air in the brake pipe maintained at a defined pressure enters the piston housing through a port at one end thereof. In this condition, air from the brake pipe engages the face of the piston to move the piston to one end of a throw along which the piston reciprocates. With the piston in this position, known as the charging position, air passes around the circumferential extremity of the piston face and passes throughout the piston housing and into the auxiliary reservoir. The auxiliary reservoir will become charged substantially to the same pressure as that in the brake pipe.
When the engineer desires to activate the air brake, pressure in the brake pipe is decreased by manipulation of an automatic brake valve in the locomotive. The reduction of pressure in the brake pipe is, in turn, sensed at the face of the piston in the housing. As a result, pressure in the auxiliary reservoir will be at a higher level than that in the brake pipe and that sensed at the face of the piston. As a result, the pressure in the auxiliary reservoir will serve to urge the piston within its housing in a direction toward a port through which pressure in the brake pipe is introduced into the housing.
The slide valve is provided with a channel which is, initially, obstructed by the graduating valve seated within a recess formed within the stem of the piston. As the piston face moves, however, it drags the stem and, concurrently, the graduating valve to open a port to allow pressure from the auxiliary reservoir to enter into the channel through the slide valve. The slide valve is, in turn, moved by the piston stem to a location in which the channel through the slide valve is in communication with both the interior of the piston housing (and the auxiliary reservoir), on the one hand, and a pipe to the brake cylinder, on the other. When the brake assembly achieves this configuration, it is said to be in an application position. Air passes from the auxiliary reservoir, through the housing, through a pipe, and into the brake cylinder to urge the brake piston, to overcome a bias, to a location at which the brake will be applied.
Discharge of air within the auxiliary reservoir/piston housing assembly to the brake cylinder will result in a reduction of pressure within the auxiliary reservoir/piston housing assembly. As this occurs, the piston head and attached stem will be urged away from the application position back toward a location intermediate the charging position and the application position. The piston stem, concurrently, drags the graduating valve along with it. The slide valve, however, remains, when the piston is in the lap position, in the same location it occupies when the assembly is in the application position. With this relationship of the various components, pressure will be maintained in the brake cylinder, since the graduating valve obstructs escape of air in the cylinder and its charging pipe through the channel formed in the slide valve. Lap position will continue to be maintained as long as no adjustment to air pressure in the brake pipe is made.
When the engineer desires to release the brake, the automatic brake valve within the locomotive will be manipulated to increase pressure in the brake pipe. This increased pressure acts upon the face of the piston and functions to return the piston to its charging position. As the piston is moved toward its charging position, a shoulder defined within the piston which is intended to engage the slide valve does, in fact, so engage the slide valve. As the slide valve is drawn back to the location it occupies in the charging position, ports are brought into registration with one another through the slide valve, to effect exhaust of the air in the brake cylinder. As the air is exhausted from the cylinder, the brake piston is returned to its withdrawn position to release the brake. It will be understood that the level to which the engineer increases the brake pipe pressure is that at which it was originally maintained (that is, the predetermined pressure maintained at the charging position) at which discussion of the braking cycle initiated.
The discussion of the prior art at this point has been restricted to a train car having an air brake system installed therewithin. It will be understood, however, that when multiple cars comprise the overall train, each individual car will have a substantially identical braking system installed. The braking system of each car is serviced by a common brake pipe extending the length of the train. As will be understood in view of this disclosure, "sequential" application and releasing of brakes of cars along the line will, to some extent, occur. This results from pressure reduction conveyance along the brake pipe and other factors.
It will be understood that the system described hereinbefore is rudimentary. Consequently, any problems inherent in such a system would be exacerbated.
In recognition of the lack of refinements and fine-tuning resulting in less than a perfect air brake system, various attempts have been made to improve upon the basic system. One improved structure is embodied in a component of a freight car braking system known as the ABD control valve. That product is one developed by the Westinghouse Air Brake Co. over twenty-five years ago. That product is described in detail in Westinghouse Air Brake Co.'s INSTRUCTION PAMPHLET G-g-5062-16 of August 1969. It will not, therefore, be discussed in detail herein other than to the extent that it is described in the DETAILED DESCRIPTION OF THE INVENTION portion of this document in illuminating the structure and operation of the present invention. The disclosure of INSTRUCTION PAMPHLET G-g-5062-16 of August 1969 is incorporated herein by reference.
It will be understood that the "SERVICE PORTION" described and illustrated in that Westinghouse document operates generally on the same principles as the basic system described hereinbefore. In the case of the ABD control valve, pressure in the brake pipe is not allowed to pass around the face of the piston in order to effect charging of the auxiliary reservoir. In fact, the face of the piston is sealed by diaphragm, and the air from the brake pipe merely operates on the face of the piston to move slide valves carried by the piston to effect registration of various ports and passageways to charging of the auxiliary reservoir and an emergency reservoir, and other functions. For example, as the piston is moved, a graduating valve carried thereby closes the port of communication between the brake pipe and the auxiliary reservoir as the ABD control valve moves from a charging configuration toward an application configuration.
Having specified these differences, however, it should again be pointed out that the ABD control valve functions substantially on the same principles as the basic system. As a result, initiation and functioning of the braking process are governed by the variation of the brake pipe pressure. Consequently, while some improvements over the basic system are achieved, there are still inherent deficiencies in the ABD control valve. Certainly, it does not provide for generally uniform and substantially instantaneous application and releasing of the brakes of all cars within a train.
It is to these dictates and problems of the prior art that the present invention is directed. It is an adaptor which is able to be used to retrofit an ABD control valve and other braking equipment structures to overcome problems of the prior art.